Multi-phase Closed Loop LC Tank Circuits

ABSTRACT

LC tank circuits can be coupled together to form closed loop oscillators. The interconnectivity of these LC tank circuits were performed by a physical connection such as a metal interconnect. The LC tank circuits may also comprise a plurality of inductors that are coupled together in parallel. These closed loop oscillators generate oscillations which have multi-phase components. Such circuits are useful for RF designs, clock generation for VLSI chips, adiabatic circuitry, analog circuitry, and high-speed digital circuitry.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to the co-filed U.S. applicationsentitled “MUTUAL INDUCTANCE IN TRANSFORMER BASED TANK CIRCUITRY”,“FABRICATION OF INDUCTORS IN TRANSFORMER BASED TANK CIRCUITRY”, and“FREQUENCY ADJUSTMENT TECHNIQUES IN COUPLED LC TANK circuits” filed onJul. 19, 2005, which are invented by the same inventor as the presentapplication and incorporated herein by reference in their entireties.

BACKGROUND OF THE INVENTION

Electronic consumer products are pushing both the bounds of computationcomplexity and high clocking frequencies. The systems that areexperiencing these problems include: VLSI (Very Large ScaleIntegration), microprocessors, ASIC's (Application Specific IntegratedCircuit), SOC (System On a Chip) and FPGA's (Field Programmable GateArrays). All of these systems operate at clock frequencies that increasedramatically each year. This higher clock frequency coupled with theincreased size of the die creates some fundamental problems in heatremoval from the die and clock distribution over the surface of the die.

The power dissipation typically follows the rule: $\begin{matrix}{P = {\frac{1}{2}{CV}^{2}f}} & (1)\end{matrix}$which for a 1 pF load being clocked at a frequency of 10 GHz is 7.2 mW.Adiabatic techniques can reduce these power dissipation levels. It wouldbe worthwhile to investigate if these techniques can be usedadvantageously to help solve these problems.

Some of the basic circuit blocks to help achieve the ability formobility, low power, and high computation require the necessity of aclock oscillator block. Tank circuits have been used to generateoscillatory clock signals. These circuits use LC (inductor-capacitor)elements to form the tank circuit and they have the adiabatic qualitythat may be used to reduce the power dissipation.

For example, U.S. Pat. No. 5,396,195 issued Mar. 7, 1995 to Gabaraproposed a basic LC tank circuit in an MOS technology. The circuitconsists of a tank circuit driven by a cross-coupled MOS circuit. Theoscillations generated by the MOS LC tank circuit fabricated in a 0.9 umCMOS technology operated with a supply voltage of 3.3V. The powerdissipation was reduced by a factor of a 10× when a capacitive load wasdriven using an LC tank circuit as compared to being driven usingconventional digital techniques. This circuit has been used in amultitude of applications ranging from wireless to on-chip clockgeneration modules. Many of the inductors used in this type of tankcircuit have the form of the horizontal planar inductor as illustratedin FIG. 1 a and FIG. 1 b. These type of inductors typically require alarge amount of area to form the inductor.

The calculation of the values of planar inductors are provided in apublished paper, “Simple Accurate Expressions for Planar SpiralInductances”, IEEE J. Solid-State Circuits, Vol. 34, No. 10, October1999, by Mohan et al., hereafter referred to as the “Mohan” reference.

In addition, the Q or quality factor of these inductors that arefabricated in CMOS are typically low. The quality factor or Q is aprimary parameters in the evaluation of tank circuits. $\begin{matrix}{Q = {2\pi\frac{{Maximum}\quad{energy}\quad{stored}\quad{in}\quad{tank}\quad{circuit}}{{Energy}\quad{dissipated}\quad{per}\quad{cycle}}}} & (2)\end{matrix}$

The Q indicates the amount of energy dissipated by the tank circuit tomaintain oscillations. The tank circuit is more energy efficient as thevalue of the Q term increases which indicates that the energy dissipatedin the tank circuit decreases. One way to decrease the dissipation is toreduce the parasitic resistance of the inductor.

An oscillator block provides the ability to regulate the flow ofcomputation data within a VLSI (Very Large Scale Integration). Forinstance, the on chip clock frequency of a high-end microprocessor isexpected to reach 10 GHz before the end of this decade. In addition, thepower dissipation for the microprocessor is expected to be about 200 W,where the clock network will consume almost half of this power or 100 W.Thus, for this microprocessor, the higher frequencies and larger powerdissipation values indicate a need to have clock circuits that caneasily generate a 10 GHz signal and should be able to reduce the powerdissipation of the clock network. The clock network of these VLSI chipstypically contains large values of capacitance that need to be driven.

Currently, H-trees are used to distribute clocks over the surface of adie. Almost half of the power dissipated in chip designs occurs in theclock network of VLSI and microprocessor chips. This is largely due tothe capacitive and resistive load of the clock network.

Several authors have addressed the clocking issue to determine achievelower power, lower skew, and higher frequency of operation.

In O'Mahony et al., a U.S. PGPUB. 2003/0001652 A1 published Jan. 2,2003, they use a hierarchical clock distribution. The clock is sent to aplurality of clock grids by way of transmissions lines, and then eachgrid distributes the clock to the load. They use salphasic clockingwhich takes advantage of standing waves along a transmission line. Theposition of the receiver points must conform to positions that aremultiple of one-half wavelength from one another dependant on the clockfrequency. This will lock the frequency of the die into a rangedependant on the half-wavelength. The loads however do not have to obeythis constraint.

In Galton et al., “Clock Distribution Using Coupled Oscillators”,Proceeding of the 1996 IEEE Inter. Symp. On Circuits and Systems, May12-15, Vol. 3, pp. 217-220, they suggest using strongly coupled RCoscillators to distribute a clock signal over the die. Their techniqueuses transmission line that can be less than a quarter of a wavelengthlong. In addition, the transmission line can be lossy to couple the RCoscillators. Injection locking is used to lock all the oscillators infrequency.

In Hall et al., “Clock Distribution Using Cooperative Ring Oscillators”,Proc. IEEE 17^(th) Conf. Advanced Research in VLSI, 1997, pp. 62-75, acooperative ring oscillator is used to distribute a clock signal withinthe die. They also provide multiple clock phases in the distribution.Their circuit expands the ring oscillator from a simple ring to anN-dimensional mesh. This array does not have to be regular. One of theconcerns is aggregation that is the non-ideal characteristic variationsof the VLSI interconnect. This is a concern since interconnect that isused to connect the inverters of the ring oscillators. This factordissipates power and introduces skew into the network.

In Wood et al., “Rotary Travelling-Wave Oscillator Arrays: A New ClockTechnology”, IEEE J. Solid-State Circuits, Vol. 36, No. 11, November2001, a rotary traveling wave oscillator array is presented. It consistsof a balanced set of transmission lines with distributed CMOS latches topower the oscillation and ensure rotation lock. A waveform propagatesalong the balanced transmission line that is looped at its ends so thatthe wave continues to propagate. In their design it is important thatcareful attention is required to guard against magnetic field couplingbetween the clock conductors since it will affect the potentialperformance of their oscillators.

The technique presented here does not need to be constrained byhalf-wavelength or quarter-wavelength considerations as in O'Mahoney orGalton. In addition, Galton suffers from loss transmission lines thatare used to couple the RC oscillators together as well as the loss inthe RC oscillator. As pointed out by Hall, the power dissipation intheir technique is an issue for two factors; the ring oscillatorsdissipates power and the propagation of the signals in the interconnectdissipate power. The technique presented here uses adiabatic techniquesto help overcome the particular losses of Hall and Galton. Finally, inWood, magnetic field coupling is an undesirable condition; the techniquepresented here thrives on magnetic field coupling.

BRIEF SUMMARY OF THE INVENTION

Clock networks and clock generation in VLSI chips is a critical issue tohigh performance circuit operation. The distribution and minimization ofpower dissipation of the clock network is an important considerationwhen designing VLSI circuits. The adiabatic behavior of resonantcircuits can be utilized to help resolve both of these designsconsiderations. Inductors and capacitors play a key role in energyrecycling and distribution. The CMOS tank circuit or oscillator servesas the fundamental building block to create, distribute and maintainhigh frequency behavior in VLSI designs at low power dissipation levels.

The basic invention is connect many CMOS tank circuits together and usethe electrical and flux linkage of the resonant circuits to achieve aunified circuit behavior that is beneficial to the generation andpropagation of clock signals over a surface region of the VLSI die.Thus, this network will distribute and synchronize a clock signal overthe surface of a die.

One aspect of this invention is to connect several tank circuitstogether to create multi-phase signal generation. Such a circuitconfiguration is useful to control the operation of a state machine oroperate on the I and Q signals within RF (Radio Frequency) circuits. Inparticular, it would be desirable to also have these signals and theircompliments. The connection of these tank circuits is formed in a loopthereby adding feedback to the circuit to preferentially obtain clocksignals at different clock phase increments.

Another aspect of the invention is to utilize the flux linkage betweenthe two inductors to synchronize the operation of tank circuits. Thestructure to obtain this behavior is known as the transformer. In itssimplest form, the transformer consists of two inductors that have amutual coupling coefficient k that can vary between 0 and 1. Lenz's lawis utilized by using the flux linkage between the two coils to influenceeach other. Thus, when two inductors are placed near each other, theflux interaction can be used to force the synchronization of two or moreLC tank circuits.

Yet another aspect of this invention is to adjust the frequency of an LCtank circuit using several different techniques. A Finite State Machine,a passive flux linkage circuit and a mechanical flux linkage circuitsare described that can be used to adjust the frequency of a system ofoscillators.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 a-b illustrates two planar inductor structures.

FIG. 1 c presents a view of a planar inductor that has a helixstructure.

FIG. 1 d depicts an equivalent circuit for the planar inductor shown inFIG. 1 a-b.

FIG. 1 e provides the calculated parameters of several inductors with awidth of 20 μm.

FIG. 1 f provides the calculated parameters of several inductors with awidth of 10 μm.

FIG. 2 a shows an inductor-capacitor circuit configured as a Colpittsoscillator and connected to a regenerative circuit.

FIG. 2 b shows a inductor-capacitor oscillator and connected to aregenerative circuit in accordance with the present invention.

FIG. 3 shows a Hartley oscillator connected to a regenerative circuit.

FIG. 4 a-f shows several examples of a regenerative circuit.

FIG. 4 g-h depicts regenerative circuits in accordance with the presentinvention.

FIG. 5 a shows circuit schematics where an inductor, capacitors andregenerative circuit are combined together.

FIG. 5 b depicts circuit schematics where an inductor, capacitors andcontrollable regenerative circuit are combined together in accordancewith the present invention.

FIG. 5 c provides a simplified circuit representation of FIG. 5 a.

FIG. 5 d illustrates a simplified circuit schematic of FIG. 5 b inaccordance with the present invention.

FIG. 6 a provides a simplified circuit representation of FIG. 5 a.

FIG. 6 b-c depicts an open loop and closed loop LC tank circuit inaccordance with the present invention.

FIG. 6 d depicts the simulated waveforms of the open loop and closedloop LC tank circuit in accordance with the present invention.

FIG. 7 a depicts a three-stage open loop LC tank circuit in accordancewith the present invention.

FIG. 7 b show the simulated waveforms of the three-stage open loop LCtank circuit in accordance with the present invention.

FIG. 7 c depicts a three-stage closed loop LC tank circuit in accordancewith the present invention.

FIG. 7 d show the simulated waveforms of the three-stage closed loop LCtank circuit in accordance with the present invention.

FIG. 8 a depicts a four-stage closed loop LC tank circuit in accordancewith the present invention.

FIG. 8 b depicts a the inductor connectivity in the four-stage closedloop LC tank circuit in accordance with the present invention.

FIG. 8 c provides the simulated waveforms of the four-stage closed loopLC tank circuit in accordance with the present invention.

FIG. 9 a depicts a five-stage closed loop LC tank circuit in accordancewith the present invention.

FIG. 9 b provides the simulated waveforms of the five-stage closed loopLC tank circuit in accordance with the present invention.

FIG. 10 a depicts a seven-stage closed loop LC tank circuit inaccordance with the present invention.

FIG. 10 b provides the simulated waveforms of the seven-stage closedloop LC tank circuit in accordance with the present invention.

FIG. 11 a depicts a balanced closed loop LC tank circuit in accordancewith the present invention.

FIG. 11 b-c shows the simulated waveforms of the balanced closed loop LCtank circuit in accordance with the present invention.

FIG. 12 a provides a balanced three-phase closed loop LC tank circuit inaccordance with the present invention.

FIG. 12 b depicts the simulated waveforms of the balanced three-phaseclosed loop LC tank circuit in accordance with the present invention

FIG. 13 a provides a two-stage balanced closed loop with activetransistors in an LC tank circuit in accordance with the presentinvention.

FIG. 13 b-c depicts a simplified circuit representation of a singlecomponent of the two-stage balanced closed loop with active transistorsin an LC tank circuit in accordance with the present invention.

FIG. 13 d provides a simplified block diagram of a two-stage balancedclosed loop with active transistors in an LC tank circuit in accordancewith the present invention.

FIG. 13 e illustrates the waveforms of a two-stage balanced closed loopwith active transistors in an LC tank circuit in accordance with thepresent invention.

FIG. 14 a provides a three-stage balanced closed loop with activetransistors in an LC tank circuit in accordance with the presentinvention.

FIG. 14 b illustrates the waveforms of a three-stage balanced closedloop with active transistors in an LC tank circuit in accordance withthe present invention.

FIG. 15 a provides a four-stage balanced closed loop with activetransistors in an LC tank circuit in accordance with the presentinvention.

FIG. 15 b illustrates the waveforms of a four-stage balanced closed loopwith active transistors in an LC tank circuit in accordance with thepresent invention.

FIG. 16 a provides a simplified circuit representation of FIG. 5 a.

FIG. 16 b depicts a regenerative circuit connected to a physicalinductor.

FIG. 17 a illustrates two instances of a regenerative circuit connectedto a physical inductor where the inductors have flux linkage inaccordance with the present invention.

FIG. 17 b illustrates a circuit representation of two instances of aregenerative circuit connected to an inductor where the inductors haveflux linkage in accordance with the present invention.

FIG. 17 c shows the simulation waveforms of two instances of aregenerative circuit connected to an inductor where the inductors haveflux linkage in accordance with the present invention.

FIG. 17 d illustrates a circuit representation of two instances of aregenerative circuit connected to a inductor where the inductors have areversed flux linkage in accordance with the present invention.

FIG. 17 e shows the simulation waveforms of two instances of aregenerative circuit connected to an inductor where the inductors have areversed flux linkage in accordance with the present invention.

FIG. 18 illustrates four instances of a regenerative circuit connectedto a physical inductor where the inductors have flux linkage inaccordance with the present invention.

FIG. 19 a depicts a circuit representation of one instance of aregenerative circuit connected to two inductors where the inductors mayhave flux linkage in accordance with the present invention.

FIG. 19 b shows the physical layout of one instance of a regenerativecircuit connected to two physical inductors where the inductors may haveflux linkage in accordance with the present invention.

FIG. 20 a depicts the physical layout of two instances of a regenerativecircuit connected to two inductors where the inductors have flux linkagein accordance with the present invention.

FIG. 20 b shows the circuit representation of two instances of aregenerative circuit connected to two inductors where the inductors haveflux linkage in accordance with the present invention.

FIG. 21 a presents the circuit representation of eight instances of aregenerative circuit connected to two inductors where the inductors haveflux linkage in accordance with the present invention.

FIG. 21 b depicts the physical layout of eight instances of aregenerative circuit connected to two inductors where the inductors haveflux linkage in accordance with the present invention.

FIG. 21 c illustrates the simulation waveforms for the physical layoutof eight instances of a regenerative circuit connected to two inductorswhere the inductors have flux linkage in accordance with the presentinvention.

FIG. 21 d illustrates a close-up region of the simulation waveforms forthe physical layout of eight instances of a regenerative circuitconnected to two inductors where the inductors have flux linkage inaccordance with the present invention.

FIG. 21 e shows a close-up region of the simulation waveforms for thephysical layout of eight instances of a regenerative circuit connectedto two inductors where the inductors have no flux linkage in accordancewith the present invention.

FIG. 21 f depicts the simulation conditions for the circuit inaccordance with the present invention.

FIG. 21 g presents the simulation results and predictive results for thecircuit in accordance with the present invention.

FIG. 22 a illustrates a circuit representation of one instance of aregenerative circuit connected to four parallel inductors where theinductors may have flux linkage in accordance with the presentinvention.

FIG. 22 b illustrates the physical layout of one instance of aregenerative circuit connected to four physical inductors where theinductors may have flux linkage in accordance with the presentinvention.

FIG. 23 a depicts a two-dimensional view of three instances of aregenerative circuit connected to a four rectangular physical inductorswhere the inductors have flux linkage in accordance with the presentinvention.

FIG. 23 b shows a two-dimensional view of four instances of aregenerative circuit connected to a four rectangular physical inductorswhere the inductors have flux linkage in accordance with the presentinvention.

FIG. 24 presents the connection of two coils each on a separate die thatare connected together using solder bumps in a MCM technology inaccordance with the present invention.

FIG. 25 a illustrates the block diagram of a balanced eight-phase clockgenerator in accordance with the present invention.

FIG. 25 b presents the circuit schematic of the block generating the φ1signal in accordance with the present invention.

FIG. 25 c depicts the physical layout of the balanced eight-phase clockgenerator in accordance with the present invention.

FIG. 25 d shows an inductor layout with extended legs in accordance withthe present invention.

FIG. 25 e illustrates a three dimensional perspective of two inductorsplaced over one another in accordance with the present invention.

FIG. 25 f presents two physical layouts of the balanced eight-phaseclock generator where one is rotated 180° in accordance with the presentinvention.

FIG. 25 g illustrates the relative placement of two physical layouts ofthe balanced eight-phase clock generator in accordance with the presentinvention.

FIG. 26 a depicts the physical layout of sixteen instances of thebalanced eight-phase clock generator where the inductors have fluxlinkage in accordance with the present invention.

FIG. 26 b shows all 64-clock output waveforms of the physical layoutgiven in FIG. 26 a during the time period around 10 nsec.

FIG. 26 c shows all 64-clock output waveforms of the physical layoutgiven in FIG. 26 a during the time period around 100 nsec illustratingthe flux linkage synchronizing all outputs in accordance with thepresent invention.

FIG. 26 d depicts the simulation conditions for the circuit inaccordance with the present invention.

FIG. 26 e presents the simulation results and predictive results for thecircuit in accordance with the present invention.

FIG. 27 illustrates the control circuitry to adjust the coarse and finecapacitance in several LC tank circuits in accordance with the presentinvention.

FIG. 28 a depicts the schematic of a passive flux linkage frequencyadjust circuit in accordance with the present invention.

FIG. 28 b shows the simulation waveforms of a passive flux linkagefrequency adjust circuit in accordance with the present invention.

FIG. 28 c illustrates the use of a varactor to adjust the frequency ofan LC tank circuit.

FIG. 28 d illustrates the use of a switched array of capacitors toadjust the frequency of an LC tank circuit.

FIG. 28 e illustrates the use of a enhancement mode transistor to adjustthe frequency of an LC tank circuit.

FIG. 28 f illustrates the use of a depletion mode transistor to adjustthe frequency of an LC tank circuit.

FIG. 29 illustrates a second control circuitry to adjust the coarse andfine capacitance in several LC tank circuits in accordance with thepresent invention.

FIG. 30 a depicts the schematic of a mechanical flux linkage frequencyadjust circuit in accordance with the present invention.

FIG. 30 b shows the simulation waveforms of a mechanical flux linkagefrequency adjust circuit in accordance with the present invention.

FIG. 30 c illustrates the MEMS cross-sectional view of a mechanical fluxlinkage frequency adjust circuit in accordance with the presentinvention.

FIG. 31 a depicts a top view of two instances of a physical layout of asingle regenerative circuit that is parallel connected to four physicalcoils in accordance with the present invention.

FIG. 31 b reveals a cross-sectional view of two instances of a physicallayout of a single regenerative circuit that is parallel connected tofour physical coils being synchronized by an external fluxlinkage-generating unit in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The LC (inductor-capacitor) tank circuit has been a fundamental buildingblock in many electrical system designs. This circuit is used inwireless, digital, and mixed-signal designs. The basic building elementsof the LC tank circuit consist of at least one inductor and and at leastone capacitor.

The invention is based on the discovery that the flux linkage betweeninductors can be used to synchronize an interwoven network formed fromindividual LC tank circuits. The flux linkage that occurs between twoinductors forms the basis of a structural unit known as a transformer.The coupling coefficient of the transformer can be utilized to lock aninterwoven network of tank circuits so they operate in-phase. Theability to phase and frequency lock the interwoven network of tankcircuits over the face of the die allows the generation of a unifiedclock waveform. The additional benefit is that the adiabatic nature ofentire interwoven network reduces the power distribution of the clocknetwork for a VLSI chip by over two orders of magnitude.

In addition, several techniques are offered to control the frequency ofoperation of the interwoven network. In one case, a coarse and fineadjust capacitance is introduced into the tank circuit to directly alterthe frequency. Another method uses a passive load in a transformerconfiguration to adjust the frequency of operation of the primary LCtank circuit. And finally, the physical placement of a coil is adjustedwithin a transformer to alter the coupling coefficient to directlyadjust the frequency of operation.

Several basic examples of an LC tank circuit having a regenerativecircuit that provides a negative resistance to compensate for theresistive loss of the inductance is provided. Three differentregenerative circuits are described, where the third version allows theintroduction of external signals to effect the operation of the circuit.

Several assumptions are initially made to simplify the analysis of theinventive entity. This helps identify the key aspects of the inventionwithout losing insight. The first one will be to assume that theself-inductances of the coils in the transformer are equal. The nextassumption will assume that the capacitive load elements in a balancedtank circuit are equal. To be more specific, if a tank circuit generatesa clock and a clock bar signal, the capacitive load attached to both ofthese nodes are identical.

It is important to understand that setting these assumptions does notlimit the range or scope of the inventive idea. Before a LC tank circuitis utilized in an actual operating system, each of the above assumptionswill need to be re-evaluated according to the specifications of thedesign parameters. Those skilled in the art will recognize that theabove assumptions do not limit the scope of the invention.

FIG. 1 a illustrates a square inductor 1-1 with one turn. Note that thisinductor has two leads, 1-4 and 1-5, or ways of physically connectingthe inductor to a circuit. The width of the metallic trace is shown asW. A two-turn inductor 1-2 is depicted in FIG. 1 b. The measurements ofthe outside diameter is shown as d_(out), while the inside diameter islisted as d_(in). In addition, the distance between traces is identifiedas S. These type of inductors can occur in an IC (Integrated Circuit), aVLSI chip, an RF (Radio Frequency) chip, a PWB (Printed Wire Board), aMEMS (Micro-Electro-Mechanical-System) die or a MCM (Multi-Chip Module).The equivalent circuit representation 1-3 of the coils 1-1 and 1-2 areprovided in FIG. 1 d. A simplified version of this equivalent circuit ofan inductor will be utilized in many of the circuits analyzed in thispaper to help describe the essential idea of this invention.

FIG. 1 c depicts a helix structure used to form an inductor 1-3. Thisinductor has two leads 1-6 and 1-7. A single turn coil 1-12 is formed ina lower metal layer, then a via 1-8 is used to connect this coil to thesingle turn coil 1-11 in an upper metal layer. The via 1-9 connects themiddle coil to the top coil 1-10 formed in an upper metal layer

The inductors 1-1, 1-2 and 1-3 are typical for the type of inductorsfound in a planar technology layout. These inductors are also calledcoils where coil can indicate that the conductor forming the inductorhas a configuration that spans a portion of 360 degrees.

In all of these planar inductors presented, several aspects were notshown. The substrate of the integrated circuit upon which these planarinductors are fabricated is not shown. In addition, the oxide ordielectric layer surrounding the metal layers is not illustrated. Thesesimplified drawings provide an easier description of the structure ofthe inductor. The integrated circuit can typically have a plurality ofmetallization and dielectric layers. In addition, only a square inductorhas been shown, however, those skilled in the art will realize that theinductor can be formed in a circular, oval, hexagonal or other shape,and still be within the scope of the invention.

Finally, the tables listed in FIG. 1 e and FIG. 1 f displays theparameters of several inductors that were determined using the “Mohan”reference. The first column lists the values of the self-inductancesL_(equ). The second column indicates N which indicates the number ofturns of the coil. The next column gives d_(out) that is the outsidedimension of the coil. The remaining dimensions of d_(in) and W are alsoindicated. Note that one difference between FIG. 1 e and FIG. 1 f isthat the width of the conductive trace used to form the coil is 20 μmand 10 μm, respectively. The number of squares forming the conductivetrace of each inductor is indicated in the sixth column. The next columnprovides the parasitic resistor assuming that the sheet resistance of0.01Ω/□ is used. Finally, the last column gives the parasiticcapacitance C_(ox) of the inductors (see (FIG. 1 d). Note that thiscapacitance value is one half of the total parasitic value of theinductor. These inductors provide an indication of the real estate usedfor several one-turn inductors. In addition, several of these inductorswill be simulated in different tank circuits to help describe theinvention.

The number of squares can be used with the sheet resistance value todetermine an approximate resistance. The skin effect typically increasesthe resistance of the inductors proportional to the square root offrequency; however, the skin resistance effect will not be addressed inthis discussion so that the concepts of the invention can be more easilyvisualized. For instance, the skin-depth in copper is about 0.66 μm at10 GHz. Because of this effect, the current is carried near the surfacecausing the resistance to increase as mentioned earlier.

An example of a Colpitts tank circuit oscillator 2-1 having aregenerative circuit 2-2 is given in FIG. 2 a. A regenerative circuit2-2 is required to replace the energy lost by the dissipative process ofenergy flow through the resistive components within the tank circuit. Ifthe regenerative circuit 2-2 was eliminated, the oscillations generatedby the tank circuit 2-1 would eventually die out because of thisresistive loss. The regenerative circuit can be formed out of activetransistors; such as MOS transistors, CMOS transistors or BJTtransistors. The regenerative circuit provides a negative resistancethat cancels the parasitic resistance in the tank circuit. Theregenerative circuit used is a type regen-1 and, in addition, has apower and ground connection. The oscillator signal is generated acrossthe two capacitors C₁ and C₂. Thus, this circuit has two outputs 2-3 and2-4 that originate from the tank circuit. The signals that are developedacross these two capacitors are 180 degrees out of phase with eachother.

FIG. 2 b illustrates a second version of the Colpitts oscillator 2-5where the regenerative circuit 2-6 of type regen-1 a has two additionalinputs 2-7 and 2-8. These inputs can be used to introduce other clocksignals into the oscillator to control its phase generation.

A Hartley oscillator 3-1 is shown in FIG. 3. In total, this circuitrequires at least two inductors. This regenerative circuit 3-2 is typeregen-2 and has a ground in this case, but as will be seen shortly mayonly contain a power connection. The regen-2 has two outputs 3-3 and 3-4that connect to the circuit.

FIG. 4 illustrates several CMOS circuits configured in either regen-1,regen-1 a or regen-2 type regenerative circuits. Similar circuits can bedesigned using BJT transistors as well. In FIG. 4 a, a regen-1 typecircuit 4-1 is shown; here a p-channel 4-2 serves as a current source tothe rest of the circuit. The two p-channel transistor 4-3 and 4-4 arecross coupled toe ach other; that is, the drain of 4-3 is connected tothe gate of 4-4 and the drain of 4-4 is connected to the gate of 4-3.This forms a regenerative circuit, note that the two transistors havethe same conductivity type. The two n-channel transistors 4-5 and 4-6are configured in a similar manner. The drain of 4-6 is connected to thegate of 4-5 and the drain of 4-5 is connected to the gate of 4-6. Thisforms a second regenerative circuit. The tank circuitry is connected tothe drains of the two cross coupled transistor circuits. In addition,the tank circuitry and the cross coupled transistors share the groundand power nodes. The output signal is provided at the two output nodes4-7 and 4-8. The negative resistance of the circuit compensates for theresistive loss in the tank circuit and allows the oscillation created inthe tank circuit to be maintained.

A regen-1 type circuit 4-9 similar to the circuit 4-2 is given in FIG. 4b except that the p-channel current source has been removed. The circuit4-9 provides the outputs 4-7 and 4-8.

An equivalent representation of the circuit 4-9 is provided in FIG. 4 c.This regenerative circuit 4-10 consists of two inverters connected headto tail as shown. This is also the basic building block of a ram-cellthat is used to store memory in integrated circuits (IC). The outputs ofthis circuit 4-10 are indicated as 4-7 and 4-8. This ram-cell has threestates; outputs 4-7 and 4-8 are equal, output 4-7 is a logic “1” whileoutput 4-8 is a logic “0”, and the case where output 4-7 is a logic “0”while output 4-8 is a logic “1”. The first state given is also know asthe meta-stable state, where both outputs are equal. A slight bit ofnoise introduced into the circuit 4-10 under the meta-stable statecondition will cause the circuit 4-10 to enter one of the remaining twostates.

The next three circuits are of type regen-2. In FIG. 4 d, only twocross-coupled n-channel transistors form the circuit 4-11 that is usedto compensate for the resistive loss of the LC tank circuit. The outputsfor this circuit are 4-13 and 4-14. These are the two nodes connected tothe LC tank circuit and any external load that is desired to be driven.

The circuit shown in 4-12 of FIG. 4 e includes an n-channel currentsource 4-13. Otherwise it is similar to the circuit of 4-11.

The circuit 4-14 illustrated in FIG. 4 f is the compliment of 4-11, thatis all the n-channels are replaced by p-channels and the VSS powersupplies (ground) replaced by VDD supplies and vice-versa.

The last two circuits are type regen-1 a circuits. FIG. 4 g shows aregenerative circuit 4-15 where a p-channel 4-16 serves as a currentsource to the rest of the circuit. The two p-channel transistors 4-17and 4-18 allow external signals to be introduced into the regenerativecircuit. A regenerative circuit consists of the two cross-coupledn-channels 4-21 and 4-22. The negative resistance of this circuit isprovided to the LC tank circuit using the two outputs 4-19 and 4-20. Thenegative resistance of the circuit compensates for the resistive loss inthe tank circuit and allows the oscillation created in the tank circuitto continue.

FIG. 4 h illustrates the second version 4-23 of the regen-1 a circuit.This circuit is similar to the circuit in FIG. 4 g, except that thep-channel current source ahs been eliminated.

FIG. 5 a depicts an LC tank circuit 5-1. It contains a regenerativecircuit generating two outputs 5-4 and 5-5 that drive two sets ofbalanced capacitive loads. A capacitor 5-2 combines all of thecapacitance that is typically non-adjustable. This may include theparasitic capacitance of wire interconnections, the capacitance of thegate, drain, overlap capacitance of the transistors forming theregenerative circuit, the capacitance of the inductors 5-4, and thecapacitance of the gates or circuits being driven by the LC tankcircuit.

The capacitor 5-3 is an adjustable capacitor that is used to adjust thefrequency of oscillation of the LC tank circuit. Some examples offrequency adjustment include a voltage-controlled varactor that can beformed using a diode or a MOS transistor. The MOS transistor can beconfigured as an enhancement or depletion mode transistor. By adjustingthe control voltage to these transistors, the capacitance presented tothe tank circuit can be modified, thereby, modifying the frequency ofoperation of the tank circuit. Another form of adjustable capacitorwould include an array of MOS transistors. The array would presentcapacitance to the LC tank circuit through switches that can becontrolled be a set of control voltages. By adjusting these voltages,one or many gates can be connected or disconnected to the LC circuitthat in turn varies the effective capacitance presented to the LC tankcircuit. The frequency of operation of the tank circuit changesaccording to equation (3) where only the values of C and L are used inthe following formula: $\begin{matrix}{f = \frac{1}{2\pi\sqrt{LC}}} & (3)\end{matrix}$

FIG. 5 b shows a LC tank circuit 5-6 where the regenerative circuit typeregen-1 a is used. Inputs 5-7 and 5-8 can be applied to the gates of thetwo p-channel transistors. This circuit generates two outputs 5-9 and5-10. Similar to the previous circuit, this circuit contains both theconstant capacitive load 5-12 and the adjustable capacitor 5-11.

FIG. 5 c presents a simplified model 5-1 of the LC tank circuit 5-1given in FIG. 5 a. In addition, the two outputs of the circuit 5-4 and5-5 are depicted. Although not shown in FIG. 5 c, the capacitive loadsillustrated in FIG. 5 a are assumed to exist in this simplerrepresentation of the circuit. The transistors have been modeled using aram-cell circuit providing a compact representation of this LC tankcircuit. The meta-stable state of the ram-cell combined with theparasitic resistance of the inductor shorting the two outputs 5-4 to 5-5appears to make the meta-stable state more likely. To overcome thisstate, a start up circuit can be used to unbalance the two outputs.Startup circuits are well known in the art and will not be describedfurther. This simple circuit representation 5-1 will be used to describeseveral inventive circuits that will be presented later.

FIG. 5 d presents a simplified model 5-6 of the circuit given in FIG. 5b. The input leads 5-7 and 5-8 are similarly labeled as before. Inaddition, the two outputs 5-9 and 5-10 are indicated.

FIG. 6 a shows the basic LC tank circuit 6-1 used to describe severaldifferent LC tank circuits, hereafter called the “basic LC tankcircuit.” This circuit has two outputs 6-2 and 6-3. The circuit alsocontains (but not shown) the capacitor network of the adjustable andconstant variety as mentioned in FIG. 5. FIG. 6 b illustrates an openseries connection 6-5 of two basic LC tank circuits. This circuit 6-5contains three outputs; 6-2, 6-3 and 6-4. FIG. 6 c depicts a closed loopconnection 6-7 of the circuit illustrated in FIG. 6 b. Note that output6-4 collapses and becomes the output 6-2.

FIG. 6 d presents a simulation 6-6 of the basic LC tank circuit, theopen and closed loop series connection of two of the basic LC tankcircuits. The 10 GHz outputs 6-2 and 6-4 overlap one another while theoutput 6-3 is 180° out of phase with the two previous outputs. Thus,there is no difference in the outputs of the waveforms 6-2 and 6-3 for asingle and dual connected basic LC tank circuit.

FIG. 7 a illustrates three basic LC tank circuits configured in an openseries connection 7-1. This circuit contains four outputs; 7-2, 7-3, 7-4and 7-5. FIG. 7 b presents the simulation results of these fourwaveforms. Because of the open connection, every other output issimilar. For example, waveforms 7-3 and 7-5 overlap each other, whilewaveforms 7-2 and 7-4 are generated 180° out of phase when compared towaveforms 7-3 and 7-5.

FIG. 7 c shows a closed loop connection of the three basic LC tankcircuits 7-6. Because the loop is closed, there are only three outputs;7-7, 7-8 and 7-9. Also, note that one possible stable state occurs whenthe three outputs can be equal to one another. To avoid this situation,a startup circuit can be used to prevent this condition as mentionedearlier.

This circuit 7-6 generates a single-ended multi-phase output that isshown in FIG. 7 d. The waveforms are labeled to correspond to the nodesof the circuit 7-6. Each output 7-8, 7-9 and 7-7 has a phase separationof 120° or; $\begin{matrix}{\theta = \frac{360{^\circ}}{n}} & (4)\end{matrix}$from the adjacent waveform where n equals the number of outputs in theclosed loop LC tank circuit. The oscillation signal can propagate eitherclockwise or counter-clockwise in the loop. Finally, the termsingle-ended implies that the outputs are not balanced. For example, thecircuit 7-6 generates waveform 7-8 but does not generate a balancedsignal that is 180° out of phase with the waveform 7-8.

FIG. 8 a illustrates a closed loop connection of four simple LC tankcircuits connected in series 8-1. This circuit has four outputs; 8-2,8-3, 8-4 and 8-5. the simulated waveforms 8-8 of these four outputs areprovided in FIG. 8 c. The waveforms corresponding to outputs 8-2 and 8-4overlap one another, while the waveforms of outputs 8-3 and 8-5 overlapeach other and are 180° out of phase with the output waveforms 8-2 and8-4.

FIG. 8 b illustrates the closed loop connection of the four inductorsjoined at the outputs 8-2, 8-3, 8-4 and 8-5. These inductors provide aninitial DC operating point to the circuit 8-1 at time equals to 0.Assuming the inductors in the circuit 8-1 were removed, the seriesconnection of the even number of ram-cells would cause the circuit 8-1to enter a stable state. That is, adjacent outputs would latch intoeither a high or low state. Thus, the inclusion of the inductors intothe circuit 8-1 provide the ability of an even number of seriesconnected LC tank to oscillate with the limitation that the generatedadjacent signals are 180° out of phase with each other.

Note that when the closed loop contains an even number of LC tankcircuits, the phase separation does not satisfy equation (4). This canbe seen by comparing the arrows 8-8, 8-9, 8-10 and 8-11 in the circuit8-1 against the plots of these outputs in the waveform simulation 8-12.When the time equals 19.92 nsec, the dotted line 8-6 is used to helpdetermine the direction of the arrows in the circuit 8-1. During time8-6, the output waveforms 8-2 and 8-4 are increasing which is indicatedby the upwards arrows 8-8 and 8-10 in circuit 8-1. Similarly, the outputwaveforms 8-3 and 8-5 are decreasing as indicated by the downward arrows8-9 and 8-11 in circuit 8-1. In effect, all of the arrows in circuit 8-1are 180° out of phase with its adjacent neighbor. Note that at time 8-7,all the waveforms coverage to a point 8-9. This corresponds to the casewhere all the transient outputs of the circuit 8-1 are equal. After thepoint 8-9, the arrows in the circuit 8-1 flip polarity.

FIG. 9 a depicts a closed loop series connection 9-1 of five basic LCtank circuits. The five outputs; 9-2, 9-3, 9-4, 9-5 and 9-6 are labeledin the circuit 9-1. The simulated waveforms for these five outputs areprovided in FIG. 9 b which also shows that the oscillation signalpropagates in a counter-clockwise direction in the loop.

FIG. 10 a depicts a closed loop series connection 10-1 of seven basic LCtank circuits. The five outputs; 10-2, 10-3, 10-4, 10-5, 10-6, 10-7 and10-8 are indicated in the circuit 10-1. The simulated waveforms forthese seven outputs are provided in FIG. 10 b which also shows that theoscillation signal propagates in a counter-clockwise direction in theloop.

FIG. 11 and FIG. 12 both present another form of an LC tank circuit. Thecircuit 11-1 in FIG. 11 a consists of a ram-cell generating outputs 11-2and 11-3, a second ram-cell generating outputs 11-4 and 11-5, a firstinductor connecting output 11-2 to 11-4 and a second inductor connectingoutput 11-3 to 11-5.

The simulation results for circuit 11-1 are provided in FIG. 11 b andFIG. 11 c. FIG. 11 b illustrates a stable state different from thatdescribed when the circuit given in FIG. 6 was covered. The circuit 11-1can end in state where the ram-cells latch their outputs into a high andlow state. FIG. 11 b shows the outputs 11-2 and 11-4 both ending in ahigh state, while the outputs 11-3 and 11-5 end in a low state. However,using a startup circuit, the circuit 11-1 can go into oscillation asindicated by the simulation results given in FIG. 11 c. When the circuit11-1 oscillates, the simulated results show that outputs 11-3 and 11-4overlap one another, while outputs 11-2 and 11-5 overlap each other andare 180° out of phase with the waveforms 11-3 and 11-4.

The circuit 12-1 in FIG. 12 a generates three balanced block signalsthat are 120° out of phase with one another. Three ram-cells are placedbetween outputs 12-2 and 12-4, 12-4 and 12-6 and 12-6 and 12-2 forming aring structure located in the upper portion of circuit 12-1. Anotherthree ram-cells are placed between outputs 12-3 and 12-5, 12-5 and 12-7and 12-7 and 12-3 forming a second ring structure. Finally, inductorsare positioned between outputs 12-2 and 12-3, 12-4 and 12-5, and 12-6and 12-7. A startup circuit insures that the circuit goes intooscillation. FIG. 12 b illustrates the waveforms at the outputs 12-2,12-3, 12-4, 12-5, 12-6 and 12-7. Note that the outputs located acrosseach inductor generate a set of balanced output oscillation signals.

FIG. 13 a illustrates two LC tank circuits 13-1 that are connected toeach other. The outputs 13-2 and 13-3 of the upper LC tank circuit arecross connected to the gates of the two p-channels 13-7 and 13-8 in thelower LC tank circuit. In addition, the outputs of the lower LC tankcircuit 13-4 and 13-5 are directly connected to the gates of the twop-channels 13-9 and 13-10 in the upper LC tank circuit. This circuit13-1 generates a quadrature signal. Note that the circuit 13-1 uses thetwo sets of the regen-1 a regenerative circuit.

The upper LC tank circuit is drawn in the simplified form 13-6 that wasgiven earlier as the circuit in FIG. 5 d and is redrawn in FIG. 13 b.The input signals 13-4 and 13-5 control the inverter symbols andcorrespond to the gates of the two p-channel transistors 13-9 and 13-10.The outputs 13-2 and 13-3 are formed across the inductor. The circuit13-6 is further simplified to the block diagram 13-11 depicted in FIG.13 c. The input signals are 13-4 and 13-5, while the output signals are13-2 and 13-3. The labeling of these signals are in agreement with thesignal names given in FIG. 13 b and FIG. 13 a.

The block diagram 13-11 is substituted for the circuits in FIG. 13 a togenerate the equivalent block diagram 13-12 depicted in FIG. 13 d. Thesimulation results for this circuit are given in FIG. 13 e. Note thatthe output signals 13-3 and 13-2 generate the balanced 0° and 180°signals, while the outputs 13-5 and 13-4 generate the balanced 90° and270° signals.

A block diagram 14-1 that generates six balanced signals 14-2, 14-3,14-4, 14-5, 14-6, and 14-7 are illustrated in FIG. 14 a. The circuit14-1 was simulated and the waveforms are presented in FIG. 14 b. Thethree sets of balanced signals are; the 0° and 180° signals 14-4 and14-5, the 60° and 240° signals 14-7 and 14-6, and the 120° and 300°signals 14-2 and 14-3.

Note that the outputs of each block feeding the next one do not crossone another as it did in the quadrature block diagram in FIG. 13 d.Thus, for an even balanced output signal generation, the outputs shouldcross an odd number of times. In an odd balanced output circuit, theoutputs should cross an even number of times.

FIG. 15 a shows a block digram of an eight balanced output clockgenerator 15-1. The outputs are 15-2 to 15-9. Simulation results of thecircuit in FIG. 15 a are given in FIG. 15 b. Note that there are fourbalanced sets of clock signals. Each output waveform is labeled tocorrespond to the output of the block diagram 15-1.

All of the previous circuits, block diagrams, and schematics providedthe connectivity of several LC tank circuits to generate oscillationswhich could have multi-phase components. Such circuits are useful for RFdesigns, clock generation for VLSI chips, adiabatic circuitry, analogcircuitry, and high-speed digital circuitry. The interconnectivity ofthese LC tank circuits were performed by a physical connection such as ametal interconnect. The next group of circuits will interconnect the LCtank circuits using the flux linkage between inductors or coils.

Coils and inductors sometimes have the similar meanings. Inductors aremetallic elements that have a self-inductance. Coils are also inductors,where the name coil can imply that the shape of the inductor has acircular twist in its physical structure. In addition, the word coil canbe used when there may be more than one inductor in the system where thetwo inductors may forma transformer. Thus, the coils share a fluxlinkage and signals can be sent between the coils using this fluxlinkage that exists in a transformer.

FIG. 16 a reproduces a circuit 16-1 that was shown in FIG. 5 c. The twooutputs are 16-2 and 16-3. The inductor 16-4 connects the two outputs.FIG. 16 b redraws the equivalent circuit but this time replaces theinductor with a metallic trace shaped as a coil 16-4. The coil has awidth W, and outside dimension d_(out), and inside dimension d_(in). Thecoil is connected to the regenerative circuit by outputs 16-2 and 16-3.Note that this coil only has one turn and the turn is rectangular andrepresents a basic cell. Those skilled in the art realize that the coilmay have a variety of shapes; circular, hexangular, spiral, etc. Inaddition, the number of turns can be a portion of one or several turns.

FIG. 17 a illustrates the physical placement for two of the basic cellsgiven in FIG. 16 b. The area covered by this structure is 2d_(out) byd_(out). Because of this placement, the flux produced by the coil 17-4is linked to the coil 17-5 and vice versa. A circuit schematic 17-1 isgiven in FIG. 17 b representing the placement of the coils shown in FIG.17 a. The circuit 17-1 illustrates the outputs of the upper regenerativecircuit 17-2 and 17-3 and the connection to the coil 17-4. The lowercoil is indicated as 17-5 and connects to a second regenerative circuitgenerating outputs 17-6 and 17-7. The coils link the upper and lowercircuits. This flux linkage is also known as mutual coupling and isindicated by the symbol M and the double arrowed line. In addition, thedots on the coils indicated the induced voltage generated in each coilaccording to Lenz's Law. The combination of the double coil, the Msymbol, the dots are referred collectively as a transformer. Insimulation tools, the coupling coefficient k is used to simulate theflux linkage. The mutual inductance M is related to the couplingcoefficient k according to:M=k√{square root over (L₁L₂)}  (5)

The circuit 17-1 was simulated and the results are indicated in FIG. 17c. The inductance of both coils was assumed to be equal (L₁=L₂) and thek in the simulator was set to 0.4. The waveforms at outputs 17-2 and17-6 overlay one another. This result also agrees with the position ofthe dots.

Furthermore, this simulation demonstrates that a clock signal can besynchronized over an area of the die. In this case, by reviewing thestructural layout of FIG. 17 a, the area is 2d_(out)×d_(out). Thus, thisillustrates one aspect of the invention: the flux linkage can be used tosynchronize a clock signal over an area of the die.

The dot position in the circuit 17-8 was modified as shown in FIG. 17 dwhere otherwise all the named nodes as compared to the circuit 17-1remain the same. The simulation results are indicated by the waveformsshown in FIG. 17 e. Now the outputs 17-3 and 17-6 overlay one another.Thus, in a transformer, the flux linkage tends to force the oscillationat the dotted terminals to have the same phase. And furthermore, theflux linkage tends to force the oscillation at the dotted and un-dottedterminals to have a phase difference of 180°.

FIG. 18 illustrates how a larger area can be encompassed by theplacement of additional basic cells that are flux linked to at least theneighboring coils. Four coils; 18-10 through 18-13 are positioned nearone another in an IC chip. The regenerative circuits generate theoutputs; 18-2 through 18-9. The total area is 2d_(out)×2d_(out). Thisconcept can be extended across the entire surface of the die.

The coil formation may occur in the upper layer metals of the die wherethe metal thickness can be made thicker so that the parasitic resistanceof the metal trace forming the inductance can be minimized. Activecircuitry which will be clocked by the oscillations generated by the LCtank circuits can be placed anywhere on the die if the active circuitrydoes not need these upper layers of metal for outing or forminginterconnections between the active circuitry. However, if the activecircuitry requires a partial use of these upper layers of metal then itwould be desirable to increase the area of the coil without necessarilydecreasing the frequency of operation.

For example, referring to FIG. 1 e, the inductor in the first row has aninductance of 0.565 nH and a d_(in) of 210 μm. The inductor in thesecond row has an inductance of 1.266 nH and a d_(in) of 460 μm. Thus,the second inductor has a little over twice the inductance but has aninternal area (d_(in)×d_(in)) that is more than four times that of thefirst inductor. Using equation (3) reveals that the second inductorwould drop the frequency of oscillation by a factor of 1/√{square rootover (2)} while the internal area increases by a factor of 4. Oneapproach to achieving a larger usable area while maintaining a higherfrequency of operation is to use parallel connections of inductors. Forexample, look at the physical layout 19-1 of FIG. 19 b showing a secondbasic cell. This cell measures 2d_(out)×d_(out). Two inductors 19-2 and19-5 are connected in parallel to a single regenerative circuit thatgenerates two outputs 19-3 and 19-4. Assume that the inductor in thesecond row of FIG. 1 e was used for the inductors 19-2 and 19-5. Theequivalent inductance of parallel-connected inductances is given by;$\begin{matrix}{{\frac{1}{L_{1}} + \ldots + \frac{1}{L_{n}}} = \frac{1}{L_{equ}}} & (6)\end{matrix}$or the equivalent inductance is determined as 0.633 nH by using equation(6). This value of inductance approaches that of the inductance given inthe first row. As mentioned earlier, the encompassed area of a single1.266 nH inductor increased the area by a factor of 4× compared to the0.565 nH inductor. Furthermore, since there are two of these encompassedareas enclosed by the inductors 19-2 and 19-5. The overall encompassedarea for this second basic cell using only one regenerative circuit isincreased by 8× when compared to the prior basic cell consisting of aregenerative circuit connected to a single 0.565 nH inductor. Also notethat the equivalent parasitic resistance of parallel-connected inductorsis decreased as given by: $\begin{matrix}{{\frac{1}{R_{1}} + \ldots + \frac{1}{R_{n}}} = \frac{1}{R_{equ}}} & (7)\end{matrix}$so the resistance presented to the regenerative circuit is 0.467Ω asdetermined by using equation (7). This is very similar to the parasiticresistance value of the first inductor in the first row. Thus, theparallel combination of larger inductances or coils in an IC offersbenefits of increasing the encompassed area. In addition, the frequencyof operation and the value of parasitic resistance can maintain theirinitial values. Furthermore, only one regenerative circuit is necessaryto drive two inductors that offers the potential benefit of decreasingthe power dissipation since one regenerative circuit has beeneliminated. These are all advantages of the second aspect of hisinvention. Although the parasitic capacitance increases by a factor oftwo, the power dissipation of driving this capacitance is adiabatic(because of the tank circuit) and is lower than the power dissipationarrived at by using equation (1).

FIG. 20 a depicts the placement of two basic cells with the physicallayout of 19-1 placed next to one another to form the physical layout20-1 shown. The coils are 20-2 through 20-5 and the two regenerativecircuits generate the outputs 20-6 through 20-9. The schematicrepresentation of the physical layout 20-1 is shown in FIG. 20 b. Thenumbering of the nodes and devices follows the convention used in FIG.20 a. In particular, note that only two sets of dots are indicated onthe transformers. Note that not all of the dots are shown so that thecircuit is simplified. For example, depending on the level of theaccuracy desired in the determination of the flux interaction (a CADtool would be a useful addition to help determine the full interaction),there will be a k coupling interaction between coil 20-2 and the threecoils 20-3, 20-4 and 20-5. A k coupling interaction will also occurbetween coil 20-3 and the two coils 20-4 and 20-5. Finally, the coil20-4 will have a k coupling interaction to coil 20-5. Thus, for theabove description there should be 6 sets of dots on the transformers.Furthermore, note that there are effectively six sets of transformers;20-2 and 20-3, 20-2 and 20-4, 20-2 and 20-5, 20-3 and 20-4, 20-3 and20-5 and finally 20-4 and 20-5. This is a very simplified fluxinteraction between each coil and the other one. A more detailed fluxinteraction would occur if each coil was broken into several segments;and each of these segments interacted with all of the remainingsegments. The number of transformers would increase dramatically thusshowing the need for a CAD (Computer Aided Design) tool that would aidin the determination of all these calculations.

FIG. 21 b illustrates a physical layout 21-1 that incorporates eight ofthe basic cells with the physical layout 19-1 given in FIG. 19 b. Eachof the eight basic cells is labeled 21-2 through 21-9. In addition, onlyone of the two outputs of each regenerative circuit is labeled 21-10through 21-17. The total size of this physical layout is4d_(out)×4d_(out). An inductor from the first row of FIG. 1 f was used;thus, the area is estimated at 1000 μm×1000 μm.

A schematic circuit for the physical layout 21-1 is given in FIG. 21 a.Again note that only a fraction of the dot pairs are indicated. Thenumbering system used to identify the components in FIG. 21 acorresponds to those used in FIG. 21 b.

FIG. 21 c provides the simulation result when the circuit of FIG. 21 ais simulated. Note that the waveforms of the eight outputs 21-10 through21-17 start up randomly and then at about 2 nsec the outputs start tosynchronize and overlap one another. As pointed by the arrow, all eightwaveforms are in unison. Thus, the flux linkage between the coils can beused to synchronize the clock oscillation circuits between severalinteracting coils over a region of a die. The flux linkage allows theclock network to exchange information so that the clock oscillationcircuits can self-align their clock outputs and become synchronized.

FIG. 21 d illustrates a close-up of the eight outputs 21-10 through21-17. The skew between these eight signals is about 3 psec. This resultis very promising since this value is only about 2.4% of the 125 psecperiod or for the clocks running at 8 GHz.

FIG. 21 e depicts the situation when all the k coupling coefficients arereduced to 0. Thus, there is no interaction between the eight LC tankcircuits. As can be seen, the waveforms of the eights outputs spread outover the period dependant only on the initial conditions that wereapplied to each LC tank circuit before time t=0.

FIG. 21 f provides a table 21-18 indicating the simulation conditionswhen the circuit in FIG. 21 a representing the physical layout 21-1 wassimulated in SPICE. The frequency of operation of the layout wastargeted at 8 GHz and is an expected frequency of future VLSI andμprocessor chips. The sheet resistance of 0.01Ω/□ was used for thecoils, while each of the inverters had a p-channel width of 30 μm and ann-channel width of 15 μm. The inductor was selected from the first rowof the table given in FIG. 1 f. The inductance of each individual coilwas 0.633 nH and had a parasitic resistance of 0.868Ω. Because twoinductors were placed in parallel in each cell, equations (6) and (7)were used to determine that the equivalent inductance and resistance is0.322 nH and 0.434Ω, respectively. The k coupling coefficient valueranged from 0.4 to 0.03 dependent on the relative placement between twocoils.

FIG. 21 g gives a table 21-19 that uses the results of the currentsimulation of the physical layout 21-1 to determine expected parameterswhen the physical layout is increased in size to a die size of 1.6cm×1.6 cm. The area of one of the eight cells in the physical layout is500 μm×250 μm. The total area of the layout 21-1 in FIG. 21 b is 1,000μm×1,000 μm, while the size of the μprocessor chip is 16,000 μm×16,000μm. This data can be used to estimate the number of cells required inthe μprocessor. In the layout 21-1, 8 basic cells were placed together.A simple calculation indicates that the μprocessor would require 2048cells to cover the surface of the die.

Each basic cell contains a regenerative circuit and as indicated earlierhas a balanced output that drives a capacitive load consisting ofparasitic and adjustable components. In this simulation, each output hadan additional capacitive load of 0.5 pF connected to each output; partof which accounts for the two parallel-connected inductors that have acapacitive load of 0.35 pF. In addition, the gate and drain capacitanceof the transistors within the regenerative circuit adds another 0.6 pF.The capacitance load that each output of the basic cell drives isapproximately is 1.1 pF while the total capacitance each cell drives is2.2 pF. However, since the transistor parasitics will not changesignificantly in a given technology, their contribution of “drivable”capacitive load will be subtracted from the 2.2 pF figure leaving about1 pF of “drivable” load. The capacitive load of the inductor was notsubtracted from this figure because it is possible that the inductor canbe fabricated off-chip (MCM, for example) and may have a lowercapacitance. Thus, the total “drivable” capacitance is 1 pF and thetotal “drivable” capacitance of the layout 21-1 would be 8 pF. Thecorresponding capacitive value for the μprocessor is 2048 pF asindicated in the table.

The power per cell was simulated to be 2 mW. Thus, the total power forthe layout 21-1 is 16 mW while the μprocessor would dissipate about 4.1W.

The idea of placing more than two parallel inductors across a singleregenerative circuit 22-1 is illustrated in FIG. 22 b. Four inductors22-4 through 22-7 are positioned in four quadrants and connected to theregenerative circuit that generates the outputs 22-2 and 22-3 located atthe origin. A schematic representation of the physical layout is shownin FIG. 22 a. The numbers correspond to the same element between the twodiagrams. This type of structure allows a large inductor (bothphysically and numerically) to be used in 22-4 through 22-7, yet due toequation (6) and (7), presents a much smaller inductance and resistanceto the regenerative circuit.

The parallel combination of inductors is useful for several reasons.First, the larger inductance value implies a physically larger inductor.For example, (see FIG. 1 e, bottom row) a 3.46 nH inductor has a d_(out)of 1250 μm. Thus, the total size of the layout 22-1 would be 2500μm×2500 μm. So, one regenerative circuit can be used to cover a largearea. Second, the parallel combination reduces the resistance value from4.868Ω to 1.434Ω. This helps reduce the size of the transistors in theregenerative circuit. The benefit is that the power dissipationdecreases two ways: 1) smaller transistors that switch a load dissipateless power, 2) the leakage current is proportional to the size of thetransistors, thus there would be less power dissipation due to leakagecurrent. Third, the parallel combination reduces the inductance andallows a higher frequency to be achieved according to equation (3).

To increase the k coupling coefficient, the adjacent inductors can beplaced over the inductors of an adjacent cell. FIG. 23 a illustrates howa multi-level metallization can be used to increase the flux linkage.Assume that the physical layout or cell 22-1 is used in FIG. 23 a. Thephysical structure 23-1 shows two cells formed on a lower metal layerwhile a third cell is formed in an upper metal layer. Note the relativeplacement of the inductors from top cell in relation to the inductors ofthe remaining two lower cells. The top cell has two physical inductors23-6 and 23-7 identified while the regenerative circuit is positioned at23-3.

The active transistors within 23-3 may in fact be located in thesemiconductor portion of the die. Thus, 23-3 can symbolically representthe regenerative circuit. In addition, there are dielectric or oxidelayers between the metal layers that are not indicated, nor is thesubstrate indicated. Those with average skill in the art will appreciatethat these layers can be incorporated without losing the meaning of thisdescription.

An inductor 23-5 from one of the lower cells is positioned under theinductor 23-6 of the top cell. In addition, an inductor 23-2 from theother lower cell is positioned under the inductor 23-7 of the top cell.Thus, the top cell has a flux linkage with two lower cells. This patterncan be extended to encompass all of the cells in both metal layers tocreate a strongly coupled interwoven flux linkage network that operatesas a single unit. A feed forward continuous flux linkage path formed bythe flux linkage and the electrical portions of the regenerative circuitwould be the energy arriving at the regenerative circuit 23-4, thenbeing electrically sent to the inductor 23-5, having a flux linkage pathto the inductor 23-6 above it, sent electrically to the regenerativecircuit 23-3, passed electrically to the inductor 23-7, having a fluxlinkage path to the inductor 23-2 below it, sent electronically to theregenerative circuit 23-8, and passed further down the chain.

A feedback continuous flux linkage path is illustrated with FIG. 23 bwhich shows an additional cell added to the top metal layer. The fourthcell has its regenerative circuits in the region 23-9. Thus, 23-9electrically drives the inductors 23-11 and 23-13. The inductor 23-11 isover inductor 23-10 driven by the regenerative circuit 23-8, while theinductor 23-13 is over the inductor 23-12 driven by the regenerativecircuit 23-4. A feedback path would occur starting from the regenerativecircuit 23-3, sending the electronic signal to the inductor 23-6, havinga flux linkage path to the inductor 23-5 below it, sending theelectronic signal to the regenerative circuit 23-4, passed electricallyto the inductor 23-12, having a flux linkage path to the inductor 23-13above it, sent electrically to the regenerative circuit 23-9, passedelectrically to inductor 23-11, having a flux linkage path to theinductor 23-10 below it, sent electronically to the regenerative circuit23-8, passed electrically to the inductor 23-2, having a flux linkage tothe inductor 23-7 above it, and finally having the electrical signalending at the regenerative circuit 23-3.

This is one of the benefits of this invention: the flux linkage betweenthe cells have feedback and feed forward paths that lock the operationof the network to oscillate in a unified fashion. All of the pathsconverge to create a circuit that synchronizes the clock signal.

FIG. 24 illustrates a MCM (Multi-Chip Module) 24-1 containing aninductor on each of the two die making up the MCM. The cross-sectionalview has been simplified to provide the crux of the idea. For example,only one metal layer is shown on each die but those skilled in the artwill appreciate that additional metal and dielectric layers can be addedto the diagram without altering the idea. The lower die contains asubstrate 24-2 and a dielectric layer 24-3 has been deposited on thesubstrate. A metal layer 24-5 with the shape of a coil (not shown) hasbeen patterned on top of the dielectric layer 24-3. The coil 24-5 hasits first lead electrically connected to a via and a metal layer 24-6.The second lead of the coil is electrically connected to the via and ametal layer 24-9. The solder bumps 24-7 connect the lower die to theupper die.

The upper die has a similar structure as the lower die to simplify thedescription and many of the numerals describing the features are thesame. A dielectric layer 24-3 is deposited on the substrate 24-2. Ametal layer 24-8 with the shape of a coil (not shown) has been patternedon top of the dielectric layer 24-3. The coil 24-8 has its first leadelectrically connected to a first via and a metal layer 24-6. The secondlead of the coil is electrically connected to a second via and a metallayer 24-9. The solder bumps 24-7 not only provide mechanical support tothe two die but electrically connect the two coils in parallel as well.These two coils are now electrically connected in parallel and the fluxof each coil is linked to the other coil due to their proximity to eachother.

So far, all of the flux linkage structures to distribute a clock signalover the surface of an IC were for one clock signal and its inverse. Itis possible to create a flux linkage network that synchronizes amulti-phase signal. The intent would be to try to isolate each of thedifferent clock phases from one another as much as possible and attemptto link up only the flux of the coils responsible for generating thesame phase clock signals. The basic circuit, which will be distributedover the surface of the die, is illustrated in FIG. 25 a which wasdiscussed earlier. This circuit 25-1 generates a set of balanced clocksignals separated by 45°. Each block 25-2,, 25-8, 25-9 and 25-10generates a set of clocks. The top block 25-2 that generates φ1 has twoinputs 25-3 and 25-4 and two outputs 25-5 and 25-8.

The circuit schematic within the top block 25-2 is illustrated in FIG.25 b. The inputs 25-3 and 25-4 are applied to the gates of the twop-channel transistors, while the two outputs 25-5 and 25-6 are generatedby the cross-coupled n-channel structure connected to the inductor 25-7.

The inductor 25-7 of the top block 25-2 is shown in its physicalstructure in FIG. 25 c responsible in part for generating the clocksignal φ1. Each of the remaining blocks 25-8, 25-9 and 25-10 contain aninductor 25-11, 25-12 and 25-13 and is used to generate the clocksignals φ2, φ3 and φ4, respectively, as indicated. The physicalstructure and the relative positioning of the three additional inductorswith respect to each other is provided in FIG. 25 c as 25-17. Note thatthe layout of each inductor contains an extension leg that is connectedto the solid square 25-14. This extension leg helps to segregate theflux within one inductor from each of the other inductors. The square25-14 symbolically contains all the transistors within the circuit 25-1with the exception of the inductors. Thus, this square 25-14 containsthe transistors, capacitors, varactors, and electrical outputs.

A single layout of the inductor with the extension leg 25-7 is indicatedin FIG. 25 d. The extension leg has two leads and carries current 25-15in both directions. If the leads are placed close together, Lenz's lawwill negate the value of the inductance of these two conductor trances;however, these trances will still add both parasitic capacitance andresistance into the circuit and needs to be accounted for duringsimulations. The square loop uses the measurements of d_(out) and d_(in)for the loop as given earlier. Assume that the extension leg has alength of ½d_(out).

The physical overlap flux linkage structure 25-16 of an inductor with aleg extension with another inductor with a leg extension is provided inFIG. 25 e. This type of layout will help to increase the flux linkagebetween the two coils, thus correspondingly increasing the couplingcoefficient k.

FIG. 25 f depicts the physical placement of two physical layouts 25-17where the second one on the right is being rotated counter-clockwise by180°. In addition, the physical representation of these layouts has beensimplified where the detail of the inductor trace has been eliminated.After the rotation, the φ3 coil of the left layout 25-17 is placed overthe φ3 coil of the right layout forming the physical overlap fluxlinkage structure 25-16. This linkage improves as the two coils arealigned over one another along their edges. The entire physicalstructure 25-18 forms the basic building cell to generate a large array.

The physical structure 25-18 is used to form the network 26-1 in FIG. 26a. Note that to build this network, the physical structure 25-18 isduplicated and the odd phases are flux linked together horizontallywhile the even phases are flux linked together vertically. This layoutis a 4×4 array having a size of 8d_(out) by 8d_(out). Each basic cellgenerates the eight balanced outputs in each of their respective square26-3. In total, this layout 26-1 generates (4)*(4)*(8) or 128 outputs.The inductors along the periphery 26-2 used to be altered in value toaccount for the boundary condition. The inductor within these peripherylocations are modified according to:L _(boundary) =L _(internal)(1+k)  (8)

The value in equation (8) uses the k coupling coefficient value for thephysical overlap flux linkage structure 25-16 of the overlapping coils.

The physical layout 26-1 was modeled and simulated in SPICE. FIG. 26 billustrates a 200 psec window at time t=10 nsec where the simulatedresults of all 128 outputs in the array are shown. These outputs appearto be randomly distributed. However, the same 128 outputs waveforms areplotted in a 200 psec window at time t=100 nsec, revealing the resultsof FIG. 26 c. The flux linkage was given enough time to synchronize thenetwork and generate the multi-phase signals that are separated 45°apart from one another. This is a fabulous result. This indicates thatflux linkage can synchronize and distribute multi-phase signals over thesurface of an IC. The measured spread of the skew at 100 nsec is 3 psec.

FIG. 26 d provides a table 26-6 indicating the simulation conditionswhen the circuit in FIG. 26 a representing the physical layout 26-1 wassimulated in SPICE. The frequency of operation of the layout wastargeted at 10 GHz and is an expected frequency of future VLSI andμprocessor chips. The process was a 0.13 μm CMOS technology having acore VDD of 1.2V. The transistor sizes in the regenerative circuit has ap-channel width of 20 μm and an n-channel width of 10 μm. Each basiccell generates 4 sets of balanced outputs and contains 4 regenerativecircuits, one for each set of balanced outputs. The inductor wasselected from the first row of the table given in FIG. 1 f. Theinductance of each individual coil was 0.633 nH and had a parasiticresistance of 0.868Ω+0.24Ω for the extension leg providing a total of1.108Ω, where a sheet resistance of 0.01Ω/□ was used for the coils. Theparasitic capacitance C_(ox) of the coil and extension leg is 0.225 pF.The k coupling coefficient value was set at 0.9.

FIG. 26 e gives a table 26-7 that uses the results of the currentsimulation of the physical layout 21-1 to determine expected parameterswhen the physical layout is increased in size to a die size of 1.6cm×1.6 cm. The area of one of the sixteen cells in the physical layoutis 500 μm×500 μm. The total area of the layout 26-1 in FIG. 26 a is2,000 μm×2,000 μm, while the size of the μprocessor chip is 16,000μm×16,000 μm. This data can be used to estimate the number of cellsrequired in the μprocessor. In the layout 26-1, 16 basic cells wereplaced together. A simple calculation indicates that the μprocessorwould require 1024 cells to cover the surface of the 1.6 cm×1.6 cm die.

Each basic cell contains four regenerative circuits and is indicatedearlier has a balanced output that drives a capacitive load consistingof parasitic and adjustable components. In this simulation, each outputhad an additional capacitive load of 0.5 pF connected to each output;part of which accounts for the inductor that have a capacitive load of0.2225 pF. Thus, the total “drivable” capacitance (discussed earlier) ineach cell is 4 pF and the total “drivable” capacitance of the layout26-1 would be 64 pF. The corresponding capacitive value for theμprocessor is 4096 pF as indicated in the table.

The power per cell was simulated to be 4 mW. Thus, the total power forthe layout 26-1 is 64 mW while the μprocessor would dissipate about 4.1W. The power dissipation for the μprocessor is similar to the previouscase mentioned earlier where only one phase is distributed within thedie. When the second stage buffers are added into the simulation, thepower estimation increases to 7.6 W. This power is over an order ofmagnitude less than what is being predicted for these die. Thesesimulations indicate that flux linkage is a very viable technique forpresent and future clocking networks of VLSI chips.

Due to processing, voltage, and temperature (PVT) variations, a methodof adjusting the frequency of the oscillators may be necessary. FIG. 27illustrates a circuit description 27-1 that can be utilized to adjustthe frequency of each individual oscillator. A coarse adjust signal isintroduced at input 27-2 and applied to all coarse adjustment capacitors27-3. Note that the oscillators generate a balanced signal so that bothoutputs need to be adjusted. There is also non-adjustable capacitor 27-4that models the transistor, inductor and interconnect wiring parasiticcapacitances. The signal 27-2 can be a digital bus signal, analog, or acombination of both. After the coarse adjustment, each oscillator isprobed for its frequency signal after being amplified by the buffer27-7. This buffer can be a diff-amp, inverter, or any high speed buffer.A finite state machine (FSM) 27-14 generates a bus signal 27-9 thatenables the mux 27-8 and enables the register 27-16. The buffer 27-7passes the signal through the enabled mux to the output signal 27-10.This signal is applied to the frequency detect circuit 27-12 whichcompares it against a reference oscillation signal 27-11. The output ofthe frequency detect determines whether the frequency is too low, withinrange, or too high and generates a signal 27-13. This signal is appliedto the FSM 27-14 which then decides what to do. If the frequency is veryfar off, the FSM 27-14 may command a change in the coarse signal 27-2,otherwise information is sent to the register 27-16 via the line 27-15so that the register is set to a weight that will adjust the fine adjustcapacitors 27-6 within the oscillator. If the frequency comparison in27-12 is acceptable, the signal 27-13 instructs the FSM 27-14 to selectthe next oscillator using the signal 27-9. This signal enables the nextbuffer to place its signal onto the lead 27-10 to be analyzed. Inaddition, the register 27-16 is disabled from being altered and thecontents it holds remains fixed which maintains the correct fine adjustvalue for the capacitors 27-6 in the first oscillator. The nextoscillator's register 27-18, for example, is enabled to get ready to setits register to the unique find adjust value.

Another form of frequency adjustment is depicted in FIG. 28 a. This is apassive capacitance flux linkage frequency adjustment circuit 28-1. AnLC tank circuit contains a regenerative circuit, an inductor 28-4 andgenerates two outputs 28-6 and 28-5. The inductor is mutually coupledvia flux linkage to a second inductor 28-3. This second inductor 28-3forms part of a tank circuit where the capacitor 28-2 forms the otherpart. The capacitor 28-2 is adjustable and by adjusting its value thefrequency of operation of the circuit 28-1 can be altered.

The simulated waveforms for this circuit 28-1 are illustrated in FIG. 28b. When the capacitance of the capacitor 28-2 is set to 1.7 pF, thewaveform 28-8 is generated which is about 13.8 GHz. When the capacitanceof the capacitor 28-2 is set to 1.0 pF, the waveform 28-7 is generatedwhich is about 5.8 GHz. Thus, by varying the capacitance of a passivecircuit that has a flux linkage to an LC tank circuit, the frequency ofoperation of the LC tank circuit can be altered.

The use of a varactor 28-10 to adjust the frequency of a oscillator 28-7is illustrated in FIG. 28 c. The oscillator outputs 28-8 and 28-9 areloaded with the capacitance of the varactor 28-10 controlled by theapplication of a DC voltage 28-11. As the voltage 28-11 is changed, thecapacitance of the varactor changes and adjusts the frequency of theoscillator.

FIG. 28 d illustrates the use of a digitally controlled capacitor 28-13and 28-14 to adjust the frequency of the oscillator 28-12. As before,the capacitive loads 28-13 are applied to the outputs 28-7 and 28-8 ofthe oscillator 28-12. The switches 28-14 control the amount ofcapacitance connected to the oscillator. As more capacitance is added,the frequency decreases.

FIG. 28 e shows the use of an enhancement mode transistor 28-16 used asan adjustable capacitor applied to the oscillator 28-15. The DC voltage28-17 controls the adjustment of the amount of capacitance applied tothe nodes 28-7 and 28-8 of the oscillator 28-15.

FIG. 28 f illustrates a depletion transistor 28-19 used as an adjustablecapacitor being applied to the nodes 28-7 and 28-8 of the oscillator28-18. A DC voltage 28-20 makes the adjustment.

Due to (PVT) variations, a method of adjusting the capacitance of theflux linkage frequency adjustment circuit may be necessary. FIG. 29illustrates a circuit description 29-1 that can be utilized to adjustthe frequency of each individual oscillator. A finite state machine(FSM) 29-14 generates a bus signal 29-9 that enables the mux 29-8. Thetop oscillator sends its frequency signal after being amplified by thebuffer 29-7 and passes the signal through the enabled mux to the outputsignal 29-10. This buffer can be a diff-amp, inverter, or any high speedbuffer. This signal 29-10 is applied to the frequency detect circuit29-12 which compares it against a reference oscillation signal 29-11.The output of the frequency detect determines whether the frequency istoo low, within range, or too high and generates a signal 29-13. Thissignal is applies to the FSM 29-14, which then decides what to do. Ifthe frequency is very far off, the FSM 29-14 may enable register 29-19by the bus 29-9. Then the FSM will issue a coarse adjust weight on bus29-2 that sets the register 29-19. This signal 29-2 can be digitalsignal or bus, analog, or a combination of both. The register 29-19outputs a signal 29-21 to the coarse adjust capacitor 29-3. Then theprocess of comparing the signal from the top oscillator against thereference oscillator 29-11 is performed in the frequency detect circuit29-12 again. This time if the frequency comparison is off less than acoarse adjust change, the FSM 29-14 can decide to reduce the frequencyslightly, keep the frequency the same or increase it slightly. Assumethat the FSM decides to alter the frequency, a signal is issued on 29-9to disable register 29-19, holding the previously determined coarseadjust values, and to enable register 29-16. Fine adjust information issent to the register 29-16 via the line 29-15. The register 29-16 issuesthe find adjust on bus 29-17 which sets the weight that will adjust thefine adjust capacitors 29-6 within the top oscillator. There is alsonon-adjustable capacitor 29-4 that models the inductor and interconnectwiring parasitic capacitances. After the fine adjustment, if thefrequency comparison in 29-12 is acceptable, the signal 29-13 instructsthe FSM 29-14 to select the next oscillator using the signal 29-9. Thissignal 29-9 alters the mux connection so that the next buffer in thenext oscillator can place its signal onto the lead 29-10 to be analyzed.In addition, the register 29-16 is disabled from being altered and thecontents it holds remains fixed which maintains the correct fine adjustvalue for the capacitors 29-6 in the first oscillator. The nextoscillator's coarse adjust register 29-20, for example, is enabled toget ready to set its register to the unique coarse adjust value.

FIG. 30 a illustrates another method of adjusting the frequency of theLC tank circuit. This is a passive mechanical flux linkage frequencyadjustment circuit 30-1. An LC tank circuit contains a regenerativecircuit, an inductor 30-4 and generates two outputs 30-6 and 30-5. Theinductor is mutually coupled via flux linkage to a second inductor 30-3.This second inductor 30-3 forms part of a tank circuit where thecapacitor 30-2 forms the other part. The flux linkage is adjustable byvarying the position of the second coil 30-3 with respect to the firstcoil 30-4. Thus, adjusting the k coupling coefficient can alter thefrequency of operation of the adjustment circuit 30-1.

The simulated waveforms for this circuit 30-1 are illustrated in FIG. 30b. When the k value is set to 0.1, the waveform 30-14 is generated whichis about 13.6 GHz. When the k value is set to 0.9, the waveform 30-13 isgenerated which is about 8.8 GHz. Thus, by varying the position of aninductor that has a flux linkage to an LC tank circuit, the frequency ofoperation of the LC tank circuit can be altered.

FIG. 30 c illustrates a MEMS (Micro Electro Mechanical System) 30-1containing an inductor on each of the two die making up the MEMS. Thecross-sectional view has been simplified to provide the crux of theidea. For example, only one metal layer is shown on each die but thoseskilled in the art will appreciate that additional metal and dielectriclayers can be added to the diagram without altering the idea. The lowerdie contains a substrate 30-2 and a dielectric layer 30-3 has beendeposited on the substrate. A metal layer 30-5 with the shape of a coil(not shown) has been patterned on top of the dielectric layer 30-3. Thisinductor has its leads connected to the regenerative circuit (notshown). A dielectric layer 30-4 is deposited on the metal layer 30-5.Two posts 30-6 are placed on the dielectric layer 30-4. A secondinductor is formed on the opposing substrate 30-12. A dielectric layer30-11 is deposited on the substrate 30-12. A coil is patterned in themeal layer 30-10. A dielectric layer 30-9 is deposited on the metal. Twoposts 30-8 are placed on the dielectric layer 30-10. The two sets ofposts form a sliding surface which allows the top substrate to movevertically in and out of the page. This displacement causes the fluxlinkage between the two inductors to change. This change causes thefrequency of the lower LC tank circuit to change that is the desiredeffect.

FIG. 31 a depicts two instances of a representation of the physicallayout 31-1 of the LC tank circuit given in FIG. 22 b. This correspondsto a single regenerative circuit connected in parallel to fourinductors. In addition, each of the inductors has an extension leg. Thislayout only generates only one balanced signal. The layout of theinductors insures that the current within the inductors flows in thesame direction (clockwise, for example) within each inductor.Furthermore, note that the two layouts minimize the flux linkage betweeneach other since there is a distance between the placement of these twolayouts 31-1.

FIG. 31 b illustrates these two physical layouts in a cross section viewof an IC. Not all the layers are shown; for example, the semi-conductinglayers where the transistors are formed are not depicted. In addition,not all the metal, poly, and oxide layers are indicated. Thissimplification only presents the crux of the invention withoutexplaining the full detail of the cross sectional view. The IC has asubstrate 31-4, and then an oxide layer 31-5 is deposited on thesubstrate. The metal conductors forming the inductors of 31-1 aredeposited next as the layer 31-6. Finally, an oxide layer 31-7 coats themetal layer.

The top structure 31-9 is placed close to the surface of the IC. Thisstructure 31-9 contains circuitry to generate RF signals. These signalscan originate from individual inductors, cavity oscillators, antennas,or other forms of RF signal generation. These signals 31-8 are appliedto the surface of the IC and are detected by the coils formed in themetallization 31-6. These signals 31-8 are used to force each of the LCtank circuits into synchronism. Thus, the external signal provides thestimulus to synchronize individual non-interacting LC tank circuits31-1. That is, although the flux linkage between the layouts 31-1 iszero, the external stimulus 31-8 can be used to synchronize theseindependent cells.

Finally, it is understood that the above description are onlyillustrative of the principle of the current invention. It is understoodthat the various embodiments of the invention, although different, arenot mutually exclusive. In accordance with these principles, thoseskilled in the art may devise numerous modifications without departingfrom the spirit and scope of the invention. For example, the inductor ina flux linkage system can be portioned into a physical layout that maybe, but not limited to, circular, hexagonal, or rectangular. In anotherexample, the MOS transistors illustrated in the regenerative circuit canbe replaced by BJT transistor to provide a negative impedance andmaintain the oscillations.

1. A closed loop oscillator, comprising: a first terminal and a secondterminal; a plurality of oscillators; wherein, each oscillatorcomprises: a first input node and a second input node; a first outputnode and a second output node; and, and LC tank circuit coupled to thefirst and second output nodes; wherein the LC tank circuit is comprisedof a plurality of inductors connected in parallel; the first terminal iscoupled to the first input node of a first oscillator; the secondterminal is coupled to the second input node of the first oscillator;and, the plurality of oscillators are coupled in series; wherein thefirst output node of a previous oscillator is coupled to one of theinput nodes of a next oscillator; the second output node of the previousoscillator is coupled to the remaining input node of the nextoscillator; the first output node of a last oscillator is coupled toeither of the first or second terminals; and, the second output node ofthe last oscillator is coupled to the remaining terminal.
 2. Theoscillator of claim 1, wherein: the LC tank circuit further comprises atleast one capacitor.
 3. The oscillator of claim 1, wherein: eachoscillator further comprises: a regenerative circuit coupled to thefirst and second output nodes.
 4. The oscillator of claim 1, wherein:each oscillator further comprises: a first component coupling the firstoutput node to a power supply node controlled by the first input node;and, a second component coupling the second output node to the powersupply node controlled by the second input node.
 5. The oscillator ofclaim 4, wherein: the first and second components are MOS transistors.6. The oscillator of claim 1, further comprising: at least one balancedpair of output signals.
 7. The oscillator of claim 6, wherein: thebalanced pair of output signals each drive a capacitor load.
 8. Theoscillator of claim 1, wherein: the first and second outputs of eachoscillator provides the balanced pair of output signals.
 9. Theoscillator of claim 8, wherein: the collection of the balanced pair ofoutput signals generates a multi-phase clock signal.
 10. The oscillatorof claim 1, wherein: the plurality of oscillators consist of an oddnumber of oscillators.
 11. The oscillator of claim 10, wherein: thefirst and second output nodes of each oscillator cross each other aneven number of times while forming the closed loop of the oscillator.12. The oscillator of claim 1, wherein: the plurality of oscillatorsconsist of an even number of oscillators.
 13. The oscillator of claim12, wherein: the first and second output nodes of each oscillator crosseach other an odd number of times while forming the closed loop of theoscillator.
 14. A method of forming a closed loop oscillator, comprisingthe steps of: selecting a plurality of oscillators where each oscillatorcomprises: a first input node and a second input node; a first outputnode and second output node; and an LC tank circuit coupled to the firstand second output nodes; wherein, the LC tank circuit is comprised of aplurality of inductors connected in parallel; connecting the pluralityof oscillators in series to form the closed loop; wherein, the firstoutput node of a previous oscillator is coupled to one of the inputnodes of a next oscillator; and, the second output node of the previousoscillator is coupled to the remaining input node of the nextoscillator; coupling the first output node of a last oscillator toeither of the first or second input nodes of a first oscillator; and,coupling the second output node of the last oscillator to the remaininginput node of the first oscillator; thereby, forming the closed looposcillator.
 15. The method of claim 13, wherein: each oscillator furthercomprises: a cross-coupled regenerative circuit coupled to the first andsecond output nodes.
 16. The method of claim 13, wherein: eachoscillator further comprises: a first component controlled by the firstinput node that couples a power supply node to the first output node;and, a second component controlled by the second input node that couplesthe power supply mode to the second output node.
 17. The method of claim13, wherein: the first and second output nodes of each oscillator candrive a capacitor load.
 18. The method of claim 13, wherein: the firstand second output nodes of each oscillator provides a balanced clocksignal.
 19. The method of claim 18, wherein: the collection of thebalanced signals generates a multi-phase clock signal.
 20. A closed looposcillator, comprising: a plurality of oscillators; wherein, eachoscillator comprises: a first input node and a second input node; afirst output node and a second output node; a first component coupledbetween a power supply node and the first output node; wherein the firstcomponent is controlled by the first input node; a second componentcoupled between the power supply node and the second output node;wherein, the second component is controlled by the second input node; anLC tank circuit coupled to the first and second output nodes; and, aregenerative circuit coupled to the first and second output nodes; and,the plurality of oscillators coupled in series to form a closed loop;wherein, the first output node of a previous oscillator is coupled toone of the input nodes of a next oscillator; the second output node ofthe previous oscillator is coupled to the remaining input node of thenext oscillator; the first output node of a last oscillator is coupledto one of the input nodes of a first oscillator; and, the second outputnode of the last oscillator is coupled to the remaining input node ofthe first oscillator.
 21. The oscillator of claim 20, wherein: the LCtank circuit further comprises at least one capacitor.
 22. Theoscillator of claim 20, wherein: an inductance of the LC tank circuit iscomprised of a plurality of inductors connected in parallel.
 23. Theoscillator of claim 20, wherein: each oscillator further comprises: aregenerative circuit coupled to the first and second output nodes. 24.The oscillator of claim 20, wherein: the first and second components areMOS transistors.
 25. The oscillator of claim 20, further comprising: atleast one balanced pair of output signals.
 26. The oscillator of claim25, wherein: the balanced pair of output signals each drive a capacitorload.
 27. The oscillator of claim 20, wherein: the first and secondoutputs of each oscillator provides the balanced pair of output signals.28. The oscillator of claim 27, wherein: the collection of the balancedpair of output signals generates a multi-phase clock signal.
 29. Theoscillator of claim 20, wherein: the plurality of oscillators consist ofan odd number of oscillators.
 30. The oscillator of claim 29, wherein:the first and second output nodes of each oscillator cross each other aneven number of times while forming the closed loop of the oscillator.31. The oscillator of claim 20, wherein: the plurality of oscillatorsconsist of an even number of oscillators.
 32. The oscillator of claim31, wherein: the first and second output nodes of each oscillator crosseach other an odd number of times while forming the closed loop of theoscillator.